Improved painting system

ABSTRACT

In a painting system comprising 1. A PAINTING ZONE (A) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (A), and 2. A PAINTING ZONE (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B), the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A) into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B). The invention is useful in reducing the volume of air exhausted from the painting system. Consequently, if such exhausted air must be treated with air pollution control devices, there results a reduction in the cost of the air pollution control devices and their cost of operation.

Unite States atent 1 Roberts et al.

[4 1 Apr. 30, 1974 IMPROVED PAINTING SYSTEM [73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,200

Primary ExaminerMeyer Perlin Assistant Examiner-Ronald C. Capossela Attorney, Agent, or FirmDavid J. Gould; Robert W. Black ABSTRACT In a painting system comprising 1. a painting zone (A) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (A), and

2. a painting zone (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B),

the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A) into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is-routed into the feed air stream for zone (B). The invention is useful in reducing the volume of air exhausted from the painting system. Consequently, if such exhausted air must be treated with air pollution control devices, there results a reduction in the cost of the air pollution control devices and their cost of operation. 7

16 Claims, 2 Drawing Figures Pam w sum 1 BF 2 IMPROVED PAINTING SYSTEM BACKGROUND OF THE INVENTION Existing painting systems often comprise a plurality of painting zones, each with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint. Usually the feed air stream is fresh air that has been filtered and possibly warmed and humidified. Often the exhaust air stream is vented directly to the atomsphere or vented to the atmosphere after it has been treated to remove paint particles and droplets.

However, many air pollution laws now require that a substantial amount of the vaporized organic liquid contained in the exhaust air stream must be removed prior to venting into the atmosphere. This is quite costly because in most paint spray systems there exits a large volume of exhaust air from the painting zones and the cost of air pollution control devices and their cost of operation is often roughly proportional to the total volume of air that must be treated.

SUMMARY OF THE INVENTION According to the present invention there is provided:

In a painting system comprising I l. a painting zone (A) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (A), and

2. a painting zone (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B),

the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A), into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).

There is also provided by this invention the following process:

In a painting process comprising 1. feeding air into painting zone (A), and exhausting air from zone (A) containing vaporized organic liquid from the drying of paint in zone (A), and

2. feeding air into painting zone (B), and exhausting air from zone (B) containing vaporized organic liquid from the drying of paint in zone (B),

the improvement comprising routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A), into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).

The present invention reduces the total volume of air that is exhausted from a paint spray system. Consequently, with respect to the air pollution control devices used with the paint spray system, there results a reduction in the cost of such devices and their cost of operation.

Other aspects of the invention will be described in the following.

DESCRIPTION OF THE INVENTION the term painting zone as used in this invention means an area where painting of articles takes place and where vaporized organic liquid is produced from the drying of the painted articles.

Any suitable painting means can be used for the present invention including spraying, brushing, dipping, etc. An especially suitable painting means is spraying.

The amount of exhaust air stream from a painting zone that can be routed depends upon several factors including the following: (1) the maximum allowable concentration of the vaporized organic liquid in the painting zone into which the exhaust air is routed, (2) the amount of vaporized organic liquid that is produced in the painting zone into which the exhaust air is routed, (3) the concentration of the vaporized organic liquid in the exhaust air that is routed, (4) the velocity of air flowing through each zone and (5) the size of each zone.

If the exhaust air from zone (A) has a low concentration of vaporized organic liquid, possibly all of it can be routed into the feed air stream for zone (B). An example of this is in the production line spray painting of automobiles where the automobiles are first painted with automated spray painting devices in one zone and then are painted by manual operators in another zone to paint areas that were missed by the automated spray painting devices and/or areas where the automated spray painting devices produced defective results.

In the zone of the manual operators, the concentration of the vaporized organic liquid in the exhaust stream will ordinarily be relatively low since the maximum allowable concentration of the vaporized organic liquid in that painting zone is limited by that which would be a health hazard to the operators. A term often used in this connection is threshold limit value, abbreviated TLV, which refers to airborne concentrations of the vaporized organic liquid and represents conditions under which it is believed that nearly all workers may be repeatedly exposed to day after day without adverse affect. Of course, if the manual operators are wearing protective suits supplied with their own fresh air system or a rebreather apparatus, the concentration of the vaporized organic liquid in the manual zone can exceed the TLV.

The concentration of the vaporized organic liquid in the zone where automated spraying takes place is ordinarily much greater than that of the zone of manual painting. This is because in the zone of automated painting, the limiting concentration of the vaporized organic liquid in the air is the lower explosive limit, abbreviated LEL, which is the concentration of vaporized organic liquid in the air that will explode when subjected to spark or flame. Since in many practical applications of spray painting, the LEL is ten or more times greater than the TLV, possibly the entire exhaust air stream from the manual spray painting zone can be routed to the automated spray zone, assuming of course that the volume and velocity of air from the manual zone is suitable for the automatic zone. Note, however, that in most painting systems, the concentration of vaporized organic liquid would not be allowed to reach the LEL but rather the concentration would not be allowed to exceed the desired safe concentration which would be some fraction of the LEL.

Even if the exhaust air stream for zone (A) has a higher concentration of vaporized organic liquid than can exist in painting zone (B), a portion of the exhaust air stream from zone (A) can be routed to zone (B), the routed amount being such an amount, however, than when mixed with the remaining feed air to zone (B) and the vaporized organic liquid produced by the painting in zone (B), the maximum allowable concentration of vaporized organic liquid in zone (B) will not be exceeded.

Of course, in some paint systems, it may be possible to route the air successively to more than one spray zone.

If an undesirable amount of paint particles and/or paint droplets are present in the routed exhaust stream air, it can be treated to remove these prior to routing by any suitable means such as filering, washing, etc.

Preferably, the separate painting zones will be substantially enclosed to thereby minimize the amount of air that is lost from the spray system, the amount of fresh air that is introduced into the spray system, and the mixing of air from one zone to another. For example in a production line painting system, often articles such as automobiles will move on some form of conveyor through a tunnel or a series of tunnels where the painting takes place. If there is only one painting zone in each tunnel, the entrance and exit of the tunnel should have a closure means such as a silhouette partition. This silhouette partition can be in the form of a wall, panel or the like having an opening in the shape of the outline of the article being painted so that the article can be conveyed through the opening with a minimum loss of air from the spraying system and a minimum of introduction of fresh air into the spraying system. If there are separate painting zones within a tunnel the zones should haveclosure means such as silhouette partitions separating the zones to thereby minimize the mixing of air from one zone to another zone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows side by side two interconnected sections of a production line for spray-painting of automobile bodies.

FIG. 2 shows a duct and related apparatus that can be used in place of duct 29 shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS This invention will be explained in detail in connection with a production line for the spray-painting of automobile bodies conveyed more or less continuously through a spray booth tunnel which contains the painting zones. In order to permit ready visualizaion of the invention, two transverse sections of the spray booth tunnel are presented side by side.

In the right hand half of the figure, an automobile body 1 is shown ona conveyor 2, with an operator 3 carrying a paint spray gun 3a, applying paint spray to the left hand side of the body, and another operator 4 applying paint spray through a gun 4a to the right hand side of the body. While the automobile body is shown on the conveyor 2 which is riding on rails, other conveying means can be used such as suspending the automobile body from a monorail. Using the terminology of the claims, the automobile body 1 and the operators 3 and 4 are within a section of the spray booth tunnel 5, i.e., zone (A).

In the left hand side of the figure is another section of the spray-booth tunnel 6, i.e., zone (B), having another automobile body 7 on conveyor 8. To the body 7 paint is being sprayed by an automatic spray amchine 9 having a spray gun 9a and another automatic machine 10 having a spray gun 10a. There is also an overhead automatic spray machine 11 having a spray gun 11a which is arranged to apply most of the paint sprayed to the roof and trunk of the automobile. These three automatic spray machines are illustrative only and there may be more or less than this number depending upon the contours of the particular automobile body.

Returning to the right hand half of the figure,feed air is drawn in through an intake hood 12 by blower 13. The air is distributed lengthwise through a wind chamber 14 above the spray booth tunnel 5 shown in the right hand view. The air passes through a conventional air filter 15 and then through an air-conditioning section 16 which contains humidifier nozzles 17, which are supplied with a controlled water supply by pipe 18. The excess water spray is picked up in water-sprayeliminator l9 and the cleaned, humidified, temperature-controlled air is passed into plenum chamber 20 which also, like the wind chamber 14 previously mentioned, extends the length of the manual spray-painting zone (A) of spray booth tunnel 5.

From the plenum chamber the air passes downward through dry filters 21 into the upper part of spray painting zone (A), and then downward past the operators and the automobile body being sprayed where it passes out through the grille floor 22 and into a water-washing region below this grille. The bottom of the spray booth tunnel containing zone (A) is in the form of a large pan 23 containing a shallow layer of water 24 that forms a pool collecting much of the particulate overspray conveyed by the downward flowing air. Water containing appropriate detergents is supplied by nozzle 25. The air passing over the surface of the water pool 24 turns upward past the eliminator plates 26 which are wetted with more water containing detergent by nozzles 27.

The exhaust air from painting zone (A), free of its overspray paint particles and some of the water-soluble vaporized organic liquid, but still conveying the majority of water insoluble vaporized organic liquid, becomes the feed air stream for painting zone (B) by being picked up by blower 28 and conveyed through duct 29 into the wind chamber 30 of the adjacent spray booth tunnel 6 shown in the left hand side of the figure. This air then passes through an air filter 31 into the plenum chamber 44 and thence downward through a final set of dry filters 32, and into painting zone (B) containing the previously mentioned automatic spray machines 9, l0, and 11. The air passing down through at this point contains whatever vaporized organic liquid remains after the washing techniques just mentioned and picks up additional vaporizedorganic liquid and overspray paint particles as .it sweeps downward past the automatic spray machines and the car body 7 and through another grilled floor 33 into a water-washing region below the spray booth tunnel containing a pool of water 35 held by pan 34 and supplied with additional water containing detergent through nozzle 45. This air passes upward past the spray eliminator baffles 36 which are wetted with more detergent-containing water by nozzles 37 and finally outward through blower 38 to exhaust stream 39 where the air containing vaporized organic liquid passes to air pollution control devices.

Each of the wind chambers 14 and 30 is separated from adjacent wind chambers by partitions as are also plenum chambers and 44 separated from adjacent plenum chambers. Likewise, painting zones (A) and (B) are separated from adjacent painting zones by silhouette partitions 41 and 42, so named because the openings cut in these partitions approximate the shape of the car body passing along on the conveyor, so that a minimum of air will pass from one painting zone to an adjacent painting zone, thereby minimizing the mixing of air containing low concentrations of vaporized organic liquid with air containing higher concentrations of vaporized organic liquid. Similarly, the waterwashing underparts of the spray booth tunnels are separated from one another by partitions generally indicated at 40 and 46. In both views of the production line lighting devices 43 are shown in cross-section.

Althoughthe figure shows two painting zones side by side, these painting zones will ordinarily be in line with one another, with the interconnecting duct 29 so arranged as to carry the cleaned air from painting zone (A) in spray booth tunnel 5 to painting zone (B) in spray booth tunnel 6.

FIG. 2 shows a duct and related apparatus that can be used in place of duct 29 shown in FIG. 1. In FIG. 2, the right side of duct 54 is connected to blower 28 shown in FIG. 1 and the left side of the duct 54 is connected to wind chamber 30 shown in FIG. 1. Items 48, 49 and 53, shown in FIG. 2, are control gates that can be used to regulate air flow. Duct 52 of FIG. 2 is the passage for the original'feed air stream for the portion of the spray-booth tunnel 6 that is zone (B). Item 55 of FIG. 2 is the intake hood associated with duct 52 and item 51 of FIG. 2 is the blower associated with duct 52. Duct 47 is the passage for the original exhaust air stream from the portion of the spray-booth tunnel 5 that is zone (A).

As shown in FIG. 2, control gates 48 and 53 are closed thereby allowing for all of the exhaust air from zone (A) to be routed into zone (B) and be used as the total quantity feed air for zone (B). Prior to the operating position shown in FIG. 2, control gate 49 would be closed and control gates 48 and 53 would be open, thereby providing for zone (A) having an original feed air stream and original exhaust air stream and zone (B) having a separate original feed'air stream and original exhaust air stream.

As can be seen by a comparison of FIGS. 1 and 2, FIG. 1 shows an embodiment of the present invention wherein (1) the ducts and related apparatus for the original feed air stream for zone (B) and (2) the ducts and therelated apparatus for the original exhaust air stream for Zone (A) have been removed because they are no longer needed due to all of the original exhaust In the usual production line for automobile body painting, there are several painting steps, for example,

a primer coat, sealer coat, and one or more topcoats. By the present invention, exhaust air coming from each of the manual painting zones, after it has been washed and filtered, if needed or desired, to remove the overspray paint droplets and particles may be distributed to any of the automatic painting zones, or to the automatic painting zones in succession, in whatever manner is most expeditious and inexpensive for the painting system, so long as the air concentrations do not exceed the threshold limiting value in the manual zones and the recognized safe fraction of the lower explosive limit in the automatic zones. Note, however, that if the manual operators are wearing protective suits, supplied with their own fresh air system or a rebreather air apparatus, the concentration of the vaporized organic liquid in the manual zone can be greater than the TLV and possibly may be the recognized safe fraction of the lower explosive limit.

The following example illustrates the invention.

EXAMPLE A production line for spray painting automobiles includes along its length two adjacent spray painting zones for applying paint of one color. The spray painting zones are located within a tunnel. In one of these zones, the automatic zone, are three automatic ma chines which together spray enough paint to produce 430 standard cubic feet per hour of vaporized organic liquid. The other zone, the manual zone, is staffed with manual operators whose spraying produce 181 standard cubic feet per hour of vaporized organic liquid. Each zone is 10 feet long, 18 feet wide, and is operated with downflow air at a velocity of 89 feet per minute past the operators and the machines, for a total air flow of 16,000 standard cubic feet per minute through each zone. The exhaust air stream from each zone is filtered to remove most particulates, such as paint spray particles and droplets, and is then vented to the atmosphere.

The concentration of the vaporized organic liquid in the manual zone where the operators are present is less than the threshold limiting value.

The vaporized organic liquid in both spray painting zones comprises hexane, naphtholite, mineral spirits, methyl'ethyl ketone, toluene, and xylene.

From Volume 2 of the 1969-1970 National Fire Codes, Section 86A, pages 92 and 93, issued by the National Fire Protection Association, the lower explosive limit of each component can be found in terms of its volume percent. The lower explosive limit of each component is multiplied by its mole fraction in the total vaporized organic liquid and the resulting products of each component are added to obtain the lower explosive limit for the vaporized organic liquid which was found to be 1.18% by volume.

It is desired to use the entire quantity of exhaust air from the manual spray painting zone as the feed air for the automatic spray painting zone. This can be done if the concentration of the vaporized organic liquid in the automatic spray painting zone does not exceed its lower explosive limit.

The sum of the vaporized organic liquid produced from both the manual spray painting zone and automatic spray painting zone is 430 181 61 1 standard cubic feet per hour. By ratioing this vapor volume flow rate to the air flow rate, one obtains the actual vaporized organic liquid concentration as 61 1 standard cubic feet/hour 100/60 minutes/hour X 16,000 cubic feet/minute 0.064% Expressed as related to lower explosive liniit this is 0.064%/l.l8% X 100 5.4% of the lower explosive limit. I

Thus one can use the entire quantity of exhaust air from the manual spray painting zone as the feed air for the automatic spray painting zone, which thereby will eliminate 16,000 standard cubic feet/minute of air containing vaporized organic liquid which would be an additional burden on air pollution control devices. Furthermore, the exhaust air from the automatic spray painting zone could then be used successively for several additional automatic spray painting zones until the concentration of vaporized organic liquid reached the limit specified in air pollution statutes or the desired safe concentration which would be some fraction of the lower explosive limit.

The invention claimed is:

1. ln a painting system comprising 1. a paintingzone (A) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (A), and

2. a painting zone (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B), the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A), into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).

2. The painting system of claim 1 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone.

3. The paint system of claim 1 wherein the painting system comprises a tunnel having the articles being painted conveyed through said tunnel, zone (A) and zone (B) located within said tunnel, a'silhouette partition separating zone (A) and zone (B), and a silhouette partition at the entrance and exit of said tunnel.

4. The painting system of claim 1 wherein the painting is done by spray guns.

5. The painting system of claim 4 wherein in painting I zone (A), painting is done by manually held spray guns and in painting zone (B) painting is done by automated spray guns.

6. The painting system of claim 5 wherein the routed exhaust air stream from painting zone (A) has paint particles and droplets removed therefrom prior to routing into the feed air stream for painting zone (B).

7. The painting system of claim 6 wherein zone (A) is separated from zone (B) by silhouette partitions.

8. The painting system of claim 5 wherein zone (A) is separated from zone (B) by silhouette partitions.

9. The painting system of claim 5 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone. 7

10. The painting system of claim 4 wherein the routed exhaust air stream from painting zone (A) has paint particles and droplets removed therefrom prior to routing into the feed air stream for painting zone (B).

11. The painting system of claim 10 wherein zone (A) is separated from zone (B) by silhouette partitions.

12. The painting system of claim 4 wherein zone (A) is separated from zone (B) by silhouette partitions.

13. The painting system of claim 4 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone. 7

14. The paint system of claim 1 wherein the volume of the original feed air stream for zone (B) is decreased by the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).

15. The painting system of claim 14 wherein the entire amount of exhaust air stream from zone (A) is routed into the feed air stream for zone (B).

16. In a painting process comprising 1. feeding air into painting zone (A), and exhausting air from zone (A) containing vaporized organic liquid from the drying of paint in zone (A), and 2. feeding air into painting zone (B), and exhausting air from zone (B) containing vaporized organic liquid from the drying of paint in zone (B), the improvement comprising routing exhaust air stream from painting zone (A) in an amount up to the total amount of exhaust air stream from painting zone (A) into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B). 

1. In a painting system comprising
 1. a painting zone (A) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (A), and
 2. a painting zone (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B), the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A), into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).
 2. feeding air into painting zone (B), and exhausting air from zone (B) containing vaporized organic liquid from the drying of paint in zone (B), the improvement comprising routing exhaust air stream from painting zone (A) in an amount up to the total amount of exhaust air stream from painting zone (A) into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).
 2. a painting zone (B) with a feed air stream and an exhaust air stream containing vaporized organic liquid from the drying of the paint in zone (B), the improvement comprising means for routing exhaust air stream from painting zone (A), in an amount up to the total amount of exhaust air stream from painting zone (A), into the feed air stream for painting zone (B), and decreasing the volume of the original feed air stream for zone (B) by an amount up to the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).
 2. The painting system of claim 1 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone.
 3. The paint system of claim 1 wherein the painting system comprises a tunnel having the articles being painted conveyed through said tunnel, zone (A) and zone (B) located within said tunnel, a silhouette partition separating zone (A) and zone (B), and a silhouette partitIon at the entrance and exit of said tunnel.
 4. The painting system of claim 1 wherein the painting is done by spray guns.
 5. The painting system of claim 4 wherein in painting zone (A), painting is done by manually held spray guns and in painting zone (B) painting is done by automated spray guns.
 6. The painting system of claim 5 wherein the routed exhaust air stream from painting zone (A) has paint particles and droplets removed therefrom prior to routing into the feed air stream for painting zone (B).
 7. The painting system of claim 6 wherein zone (A) is separated from zone (B) by silhouette partitions.
 8. The painting system of claim 5 wherein zone (A) is separated from zone (B) by silhouette partitions.
 9. The painting system of claim 5 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone.
 10. The painting system of claim 4 wherein the routed exhaust air stream from painting zone (A) has paint particles and droplets removed therefrom prior to routing into the feed air stream for painting zone (B).
 11. The painting system of claim 10 wherein zone (A) is separated from zone (B) by silhouette partitions.
 12. The painting system of claim 4 wherein zone (A) is separated from zone (B) by silhouette partitions.
 13. The painting system of claim 4 wherein at least a portion of the exhaust air stream from zone (B) is routed to the feed air stream of at least one other painting zone.
 14. The paint system of claim 1 wherein the volume of the original feed air stream for zone (B) is decreased by the amount of the exhaust air stream from zone (A) that is routed into the feed air stream for zone (B).
 15. The painting system of claim 14 wherein the entire amount of exhaust air stream from zone (A) is routed into the feed air stream for zone (B).
 16. In a painting process comprising 